1. Field of the Invention
The present invention relates to a multiple-resolution image scanning apparatus, particularly to a multiple-resolution image scanning apparatus which offers at least two optical resolutions for various types of image data.
2. Description of Related Art
Conventionally, data of different types are read by image scanning apparatuses of different resolutions and with different areas. For example, normal text is usually read from an A4 area with a resolution of 300 dpi. For color photographs, 4 inch and 600 dpi are regularly used values for size and resolution. Slides and negative films require a resolution of 1200 dpi for satisfactory results, but typically only a size of about 6 cm.
Conventional image scanning apparatuses aim at only one application for a certain image data type. Most image scanning apparatuses on the market are designed for A4 areas at a comparatively low resolution. For scanning photographs, image scanning apparatuses with a smaller scanned area and higher resolution are available. Any user purchasing an image scanning apparatus needs to consider the intended application and decide which type of image scanning apparatus is most suitable. For various applications, several image scanning apparatuses are needed, which is not convenient.
For overcoming the deficiency of conventional image scanning apparatuses of only one application, multiple-resolution image scanning apparatuses have appeared on the market. For example, Taiwan patent no. 232398 "Multiple lens switching system" reveals such an image scanning apparatus. By switching between various lenses, the resolution is varied. However, the various lenses are arranged nearly in a row, in front of each other, making the volume needed large.
Therefore, under Ser. No. 08/851,764 "Multiple resolution image scanning module", a multiple-resolution image scanning apparatus has been taught, which comprises: a detector (charge-coupled device); a light source; a gliding system with rails and a gliding seat gliding thereon; at least two lenses with different optical resolutions and at least two mirror groups, corresponding thereto. The at least two lenses are mounted on the gliding seat. The mirror groups are all or partly mounted on the gliding seat, too. By moving the gliding seat, the at least two lenses and the corresponding mirror groups are alternatively brought into the light path between light source and charge-coupled device, allowing for changing resolutions and scanned areas. Since for changing resolutions the light path is varied by moving the corresponding mirror groups along with the lenses, the volume required is about the same as for conventional single-resolution image scanning apparatuses.
However, the multiple-resolution image scanning apparatus revealed under Ser. No. 08/851,764 "Multiple resolution image scanning module" allows only for a single carrier for a scanned object, which still means a restriction of scanned data types. Objects to be scanned at different resolutions are laid on the same position, but with different scanned areas. The appropriate position of the lenses and mirror groups is hard to find, limiting the number of applicable lenses and mirror groups.